This invention relates to a method, software, and system for determining temperature of a physical medium. More particularly, the method, software, and system determine the temperature based on received signal information from a received signal.
Temperature in a physical medium such as a cloud is a factor in many weather related and also non-weather related applications. One weather-related application is a detection of supercooled liquid water in a cloud region for aircraft safety. Due to icing conditions of the supercooled liquid water, the cloud with supercooled liquid water can be hazardous for aircraft flying through the cloud. Supercooled liquid water clouds with large droplets (30-400 xcexcm) can cause substantial loss of climb capability. Thus, detection of supercooled liquid water in clouds is critical so aircraft can avoid hazardous clouds.
Previous research has been performed for characterizing icing conditions such as the presence of supercooled liquid water. The research suggests that median volume diameter (MVD), liquid water content (LWC), and temperature are three important parameters that characterize the icing condition for supercooled liquid water.
Prior systems use radiometer and dual-frequency radar for detecting icing conditions. One prior system includes microwave radiometers that are ground or aircraft based to detect liquid water path. Unfortunately, one disadvantage of the microwave radiometer is that no range resolution is provided. Radiometers are also used to measure temperature, but the results are not proven for cloudy conditions. One prior system uses Lidars to measure drop size distribution. This Lidar is susceptible to large attenuation and hence their range is limited. Systems that use single frequency radar measure reflectivity with fine resolution but do not provide drop size and LWC.
The size of cloud droplets can range from a few micrometers to an order of a millimeter. The characteristic size such as MVD is used to define icing condition. However, size cannot be obtained from dual-frequency radar measurements unless assumptions for temperature and drop size distribution with only two measurements are made. One publication defines radar estimated size (RES) and shows that RES is more sensitive to icing condition than MVD. The publication also illustrates a method of retrieving LWC and RES based on dual-frequency radar measurements with an assumption of the temperature.
Since liquid cloud droplets are usually small and spherical, the polarimetric measurement is less useful except for the cloud with ice or in the mixed phase. Another prior system uses a dual-frequency radar technique to determine LWC through differential attenuation. This system uses dual frequency radar beams onboard an aircraft to determine the presence, amount, and location of liquid water in a cloud. The system determines the presence of liquid water based on the difference the liquid water attenuates the two radar signals with two different attenuation characteristics. This system is also used for detecting hail and delineating regions of liquid and ice. The system additionally uses a temperature sensor to provide ambient temperature information. One problem with this prior system is the temperature sensor only measures the temperature in the immediate vicinity of the aircraft and not in the cloud where the liquid water resides. Thus, the temperature sensor provides inaccurate temperature readings of the cloud.
Another prior system uses a satellite to measure temperature of a cloud based on natural emissions of the cloud. One deficiency of this system is the satellite only measures the temperature at the top of the cloud. Another prior system called Radio Acoustic Sounding System (RASS) transmits sound waves towards an object. The RASS then receives sound waves scattered or reflected off the object to determine temperature. One disadvantage of RASS is RASS only performs optimally in fair or clear weather conditions.
Another prior system collects radar measurement from 2.8 GHz (S band), 33.12 GHz (Ka band) and 94.92 GHz (W band) frequencies from an ice-phase cloud. The system uses a neural network to estimate median particle size and peak number concentration in ice-phase clouds. One shortcoming of this prior system is the absence of temperature determination. Also, the system only applies to ice-phase cloud and not liquid clouds.
Unfortunately, all of these prior systems either assume temperature or calculate temperature imprecisely. There is a need to accurately determine temperature at any given point in a physical medium such as a cloud.
The invention solves the above problems by determining temperature of a physical medium using remote measurements. A remote measurement is a measurement where the receiver and the object to be measured are not in the same location. One example of a physical medium is a cloud. A receiver receives at least one first received signal from an interaction of at least one first transmitted electromagnetic signal with the physical medium. A processing system then determines the at least one first received signal information based on the at least one first received signal. The processing system then determines the temperature of the physical medium based on the at least one first received signal information.
In one embodiment of the invention, the receiver generates and transmits the at least one first transmitted electromagnetic signal into the physical medium. In another embodiment, the processing system determines a specific mass of the physical medium. In another embodiment, the processing system determines a characteristic size of the physical medium.
In another embodiment, the receiver receives a second received signal from the interaction of a second transmitted electromagnetic signal with the physical medium. The receiver also receives a third received signal from the interaction of a third transmitted electromagnetic signal with the physical medium. The processing system determines a second received signal information based on the second received signal. The processing system determines a third received signal information based on the third received signal. The processing system then determines a first attenuation difference based on the first received signal information and the second received signal information. The processing system determines a second attenuation difference based on the first received signal information and the third received signal information. The processing system then determines a ratio of the first attenuation difference and the second attenuation difference. The processing system finally determines the temperature of the physical medium based on the ratio.
The invention advantageously determines temperature accurately at any given point in a physical medium such as a cloud. In one embodiment, one advantage is the accuracy in temperature assists in detection of supercooled liquid water for aircraft safety because attenuation and scattering in clouds strongly depend on the temperature.